1. Field of the Invention
The present invention relates in general to a method of fabricating a liquid crystal display (LCD). In particular, the present invention relates to a method of forming an opening-free ITO (indium tin oxide).
2. Description of the Related Art
ITO is generally used as electrode or contact layer in LCD technology. When the ITO is deposited, in order to prevent the ITO from becoming poly-ITO, thereby rendering the etching of the ITO incomplete and resulting in an ITO to ITO short, the thickness of the ITO is controlled at 400 xcexcm or thereabouts. However, the thin ITO has a distinct disadvantage. The thin ITO crosses the second metal layer (about 3000 xcexcm), whose taper easily causes opening. If the second metal layer is a tri-layered metal layer, it easily comes across under cutting, inducing the ITO to open.
FIG. 1 depicts the ITO with an opening according to the prior art. A first metal layer (not shown) used as a gate is formed on a substrate 10. A gate insulating layer 14 is formed thereon.
A second metal layer 16, the tri-layered metal layer of Mo(16a)/Al(16b)/Mo(16c), is formed on the gate insulating layer 14. An insulating layer 18, used as passivation layer, is formed thereon. Then an ITO layer 20 with a thickness of 400-500 xcexcm is deposited on the insulating layer 18. When etching the metal layer 16, a Mo/Al/Mo tri-layered structure, the Al layer 16b has under cutting (labeled as 22), causing the insulating layer 18 to produce tear-drops, or recesses, 24. This occurs because the material of the middle Al layer 16b is different from the other two layers 16a and 16c. Moreover, the ITO layer 20 is so thin that it easily opens at the tear-drops 24, therefore affecting the electrical properties of the whole structure.
Additional prior art, intended as a solution, is shown in FIG. 2. The second metal layer 36 corresponding to the edge of the ITO layer 40 is designed in a twisting pattern to enlarge the circumference in the area to enhance the effectiveness of the contact area of the ITO layer 40. However, actual opening is not completely prevented. Hence, prior art cannot thoroughly resolve the opening of the ITO layer 40.
The object of the present invention is to provide a method to prevent the ITO from opening at the tapered edge of the underlayer.
To achieve the above-mentioned object, a method to prevent an ITO from opening, comprising the following steps is provided. A dummy material layer with tapered edges is formed on a substrate. A first insulating layer is formed on the dummy material layer. A metal layer is formed on the first insulating layer, one edge of the metal layer corresponding to one of the tapered edges of the dummy material layer and the other tapered edge situated away from the edge of the metal layer. A second insulating layer is formed on the metal layer. An ITO layer without opening around the edge of the metal layer is formed on the second insulating layer.
According to the embodiment of the present invention, the dummy material layer is metal and the thickness of the ITO layer is between 400 xcexcm and 500 xcexcm. Moreover, a gate can be formed with the dummy material layer, that is, both the gate and the dummy material layer belong to the first metal layer.
If the above-mentioned method is used to form a bottom gate structure, an etching stop layer, made of silicon nitride, is formed substantially corresponding to the dummy material layer on the gate insulating layer.